Toposcopy has been shown to be a viable means to catheterize small, tortuous vascular and gastrointestinal vessels. These regions have been inaccessable by existing techniques. Continuing developmental work will optimize catheter material properties, design parameters, and system configuration for diverse clinical applications. The toposcopic element everts from the tip of a conventional catheter. This extremely flexible polyurethane element has been fabricated in 3, 4, and 5 French sizes mated with 5, 6, and 7 French catheters, respectively, and is capable of eversion lengths in excess of 30 cm. The present system design facilitates sterilization and maximizes safety, reliability, and reconfigurability for clinical investigations. The design of a completely automated system is underway. Human use has continued from May 4, 1983 with the local delivery of a chemotherapy agent to brain tumors. Treatment is provided by positioning the conventional catheter in the internal carotid artery from a femoral entry, everting the toposcopic element through the carotid sinus and beyond the opthalmic artery to avert retinal toxicity, and perfusing the tumor through the middle and/or anterior cerebral arteries. Note that a conventional catheter cannot safely negotiate the tortuosity of the carotid sinus. Localized chemotherapy of other tumor locations, delivery of embolizing agents, and treatment of other vascular lesions are contemplated. The toposcopic catheter is also under modification for gastrointestinal placement through the fiber optic endoscope. The toposcopic element has successfully negotiated the convoluted cystic duct, aspirating pure bile from a catheter entry at the exposed canine papilla of Vater. Envisioned uses for the catheter are sampling of pancreatic, gal bladder, and hepatic secretions for clinical research and infusions for dissolving gall stones in situ.